Interferometers are important elements of optical circuits, and are used, for example, to provide a wavelength selection function, routing functions, analysis functions, interrogation functions, switching etc. Such devices work by providing two pathways for the incoming light which are of slightly different optical length. The two pathways then recombine, at which point interference effects occur and wavelength selection, for example, is achieved.
A major difficulty with fabricating such interferometers is that silicon has a refractive index that varies with temperature, as do most optical materials. Thus, devices using imbalanced optical paths with a nominally fixed length will have a transmission characteristic which will vary with temperature.
This temperature variation is commonly alleviated either by using thermo-electric coolers or by heating the entire optical component to a specified temperature. Thermo-electric coolers are expensive, whilst it is often undesirable to heat the component.